A Few Notes about Structure-Borne Sound
Most typically, sound levels are cited on data sheets in db(A). This means the sound level is adjusted by a curve that reflects the sound response of the human ear, the A-weighting curve. But this value only encompasses sound emitted through the air. Alas, it becomes almost meaningless for assessing the sound level of a fan mounted in a case.
In addition to emitted sound, there is also structure-borne sound to consider. What is structure-borne sound? It consists mostly of low-frequency vibrations that emanate from the motor and bearing, and are conducted from the fan to the case via the fan mount. A large chassis surface then dissipates these vibrations into the air like a loudspeaker membrane. Stiff, high-quality cases bleed out less sound from this phenomenon than flimsy ones. In addition to the loudspeaker effect, an enclosure's interior can act as a resonance chamber, aggravating the effect.
Correctly Decoupling Case Fans
Here’s the bad news: decoupling frames only benefit one entity, the vendor who sells them, since their mounting screws conduct most of the sound anyway. Rubber/silicone bolts or screws are much better because they barely conduct sound. Used together with a thin, flat gasket from the plumbing aisle of Home Depot, you get a perfectly decoupled fan. Be sure to use soft bolts instead of regular fan screws.
Fans with a Soft Rubber Frame
Companies like Xilence, Deepcool, and Noiseblocker offer case fans with a fan frame made of rubber, which can be screwed to a case without further ado. The whole frame decouples the fan noise, rendering rubber bolts unnecessary. A modern example is the 2CF from Xilence:
- A Foundation For Case Cooling: Fans
- Case Fans: Air Flow And Noise Level
- Case Fans: Decoupling Done Right
- Case Fans: Speed Control
- Case Fans: Should You Worry About Positive Or Negative Pressure?
- Case Fans: Recommendations
- CPU Coolers: Selection And Installation
- CPU Coolers: The Right Thermal Paste
- CPU Coolers: Applying Thermal Grease
- CPU Coolers: Initial Startup And Test Run
- VGA Coolers: We Rescue A GeForce GTX 480
- VGA Coolers: Single-Slot Whisper Cooler
- Think About Cooling Early